I found this on my car window whille visiting family in South Jersey. I first though it was a leaf but I took a closer look an have no idea what it is. I took pictures and asked practically everyone I know have they ever seen one. All I get is no. I was lucky because it was on my car window so I opened the door and got belly shots this part looks like an alien. I have a picture of the top but can only upload one.
I believe your caterpillar is the Monkey Slug (Hag Moth Larva) – Phobetron pithecium, of the family Limacodidae. It is about the size of a large thumb nail. The curly “arms” are actually just lobes of hairy flesh atop the caterpillar. If you turn the caterpillar over you’ll see the usual legs and head,as shown in your picture. It very often is mistaken for a leaf gall.
Those hairs on the “arms” are capable of stinging, so this caterpillar is very well defended.